High-Energy "Trap" Found In The Center Of The Milky Way

Scientists have discovered that the center of our galaxy may trap some of the highest-energy cosmic rays, producing bursts of gamma-rays that head our way.

The study was carried out by an international team of astronomers, using data from the High Energy Stereoscopic System (HESS) in Namibia and NASA’s Fermi Gamma-ray Space Telescope in, well, space. The findings are published in the journal Physical Review Letters.

Cosmic rays are high-energy particles that move through space at almost the speed of light, usually originating from things like supernovae. About 90 percent are protons, and when they interact with matter, they can produce the highest-energy form of light – gamma-rays.

Using Fermi and HESS, the team found evidence for extreme activity of gamma rays in the galactic center. Specifically, they found a glow that reached 50 trillion electron volts (TeVs). Visible light, for comparison, usually only reaches about two to three electron volts.

So, what’s going on? Well, Francis Reddy from NASA’s Astrophysics Science Division told us the trap is thought to be caused by gas clouds. As the cosmic rays make their way into the galaxy, these clouds force the highest-energy cosmic rays to move slower. At this point, the interaction of the particles and the gas releases the very high-energy gamma rays seen by the researchers.

“It remains a mystery where these extremely energetic cosmic rays are being accelerated, but when they pass through the galactic center they are slowed more than expected,” he said.

According to lead author Daniele Gaggero from the University of Amsterdam in a statement, this study suggests that most of the cosmic rays in the innermost region of our galaxy come from beyond the galactic center. It is only once they reach the center that they are then slowed down through interactions with the gas clouds, or more specifically the bulge of the galaxy itself.

“The reason for this phenomenon is not clear, but it should be explained in the context of the physics describing the interaction of cosmic rays with the galactic magnetic field,” Gaggero told IFLScience.

Interestingly, this research could also explain where neutrinos – neutral subatomic particles with masses of almost zero – are coming from. They are the fastest, lightest, and least understood fundamental particles, but because they barely interact with matter it’s tough to work out their origins.

“The findings from Fermi and HESS suggest the galactic center could be detected as a strong neutrino source in the near future, and that’s very exciting,” said Regina Caputo, a Fermi team member who was not involved in the study, in the statement.

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